fix(skills): preserve transparency in composed PowerPoint slides (#7312)

* fix(skills): preserve transparency in composed PowerPoint slides

* ci(skills): run public skill regressions

* ci: remove public skill test workflow

* docs: move skill test commands out of inherited guidance

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

CONTRIBUTING.md

@@ -338,6 +338,10 @@ before review.
 ## Testing
 
 ```bash
+# Public skill scripts (from the repository root)
+python -m pip install -r tests/skills/requirements.txt
+python -m pytest tests/skills -q
+
 # Default backend tests (four parallel shards; excludes live and blocking-I/O tests)
 cd backend
 make test

README.md

@@ -1551,6 +1551,8 @@ view. Built-in and user-created/imported skills are listed separately. The
 Community tab supports importing `.skill` archives into My skills.
 General preferences remain in Settings.
 
+The **ppt-generation** skill preserves transparent slide images when composing a presentation, including grayscale and palette PNG transparency.
+
 Administrators can see **Could not load** warnings in Capability Center > Skills
 when their own custom skill's `SKILL.md` contains invalid YAML. Warnings show the
 package-relative file and, when available, its line and column, with a quoting

skills/public/ppt-generation/SKILL.md

@@ -146,6 +146,8 @@ python /mnt/skills/public/image-generation/scripts/generate.py \
 
 After all slide images are generated, call the composition script:
 
+Transparent slide images retain their alpha channel in the presentation. Opaque images are embedded as JPEG as before.
+
 ```bash
 python /mnt/skills/public/ppt-generation/scripts/generate.py \
   --plan-file /mnt/user-data/workspace/presentation-plan.json \

skills/public/ppt-generation/scripts/generate.py

@@ -60,8 +60,11 @@ def generate_ppt(
 
         # Load and process image
         with Image.open(image_path) as img:
-            # Convert to RGB if necessary (for PNG with transparency)
-            if img.mode in ("RGBA", "P"):
+            image_format = "JPEG"
+            if "A" in img.getbands() or "transparency" in img.info:
+                img = img.convert("RGBA")
+                image_format = "PNG"
+            elif img.mode == "P":
                 img = img.convert("RGB")
 
             # Calculate dimensions to fill slide while maintaining aspect ratio
@@ -88,12 +91,16 @@ def generate_ppt(
 
             # Save processed image to bytes
             img_bytes = BytesIO()
-            img.save(img_bytes, format="JPEG", quality=95)
+            img.save(img_bytes, format=image_format, quality=95)
             img_bytes.seek(0)
 
             # Add image to slide
             slide.shapes.add_picture(
-                img_bytes, left, top, Inches(new_width_emu / 914400), Inches(new_height_emu / 914400)
+                img_bytes,
+                left,
+                top,
+                Inches(new_width_emu / 914400),
+                Inches(new_height_emu / 914400),
             )
 
         # Add speaker notes if available in plan

tests/skills/requirements.txt

@@ -0,0 +1,7 @@
+# Standalone public skill tests; no backend or model credentials required.
+duckdb==2.0.0
+openpyxl==3.1.5
+Pillow==12.3.0
+pytest==9.1.1
+python-pptx==1.0.2
+requests==2.34.2

tests/skills/test_ppt_transparency.py

@@ -0,0 +1,72 @@
+"""Slide composition preserves transparency in the embedded image."""
+
+import json
+import runpy
+from io import BytesIO
+from pathlib import Path
+
+import pytest
+from PIL import Image
+from pptx import Presentation
+
+SCRIPT = (
+    Path(__file__).resolve().parents[2]
+    / "skills/public/ppt-generation/scripts/generate.py"
+)
+
+
+@pytest.mark.parametrize("mode", ["RGBA", "LA", "P", "RGB", "L"])
+def test_ppt_preserves_png_transparency(tmp_path, mode):
+    source = tmp_path / "slide.png"
+    if mode == "P":
+        image = Image.new("P", (64, 64), 0)
+        image.putpalette([0, 0, 0, 240, 80, 40] + [0] * 762)
+        image.putpixel((48, 32), 1)
+        image.save(source, transparency=0)
+    elif mode in {"RGB", "L"}:
+        image = Image.new(mode, (64, 64), 0)
+        image.putpixel((48, 32), (240, 80, 40) if mode == "RGB" else 160)
+        image.save(source, transparency=(0, 0, 0) if mode == "RGB" else 0)
+    else:
+        image = Image.new(mode, (64, 64), (0, 0, 0, 0) if mode == "RGBA" else (0, 0))
+        image.putpixel((48, 32), (240, 80, 40, 128) if mode == "RGBA" else (160, 128))
+        image.save(source)
+    image.close()
+    with Image.open(source) as original:
+        expected = original.convert("RGBA")
+
+    plan = tmp_path / "plan.json"
+    plan.write_text(
+        json.dumps({"slides": [{"title": "Transparent slide"}]}), encoding="utf-8"
+    )
+    output = tmp_path / "slides.pptx"
+    generate_ppt = runpy.run_path(str(SCRIPT))["generate_ppt"]
+
+    generate_ppt(str(plan), [str(source)], str(output))
+
+    presentation = Presentation(output)
+    picture = presentation.slides[0].shapes[0]
+    with Image.open(BytesIO(picture.image.blob)) as embedded:
+        assert embedded.format == "PNG"
+        assert embedded.convert("RGBA").tobytes() == expected.tobytes()
+    assert (
+        "Title: Transparent slide"
+        in presentation.slides[0].notes_slide.notes_text_frame.text
+    )
+
+
+@pytest.mark.parametrize("mode", ["RGB", "L", "P"])
+def test_ppt_keeps_opaque_images_as_jpeg(tmp_path, mode):
+    source = tmp_path / "slide.png"
+    with Image.new(mode, (64, 64), 100) as image:
+        image.save(source)
+    plan = tmp_path / "plan.json"
+    plan.write_text("{}", encoding="utf-8")
+    output = tmp_path / "slides.pptx"
+
+    runpy.run_path(str(SCRIPT))["generate_ppt"](str(plan), [str(source)], str(output))
+
+    picture = Presentation(output).slides[0].shapes[0]
+    with Image.open(BytesIO(picture.image.blob)) as embedded:
+        assert embedded.format == "JPEG"
+        assert embedded.size == (64, 64)